1. Field of the Invention
This invention relates to an optical apparatus or an apparatus for detecting the direction of the line of sight of an eye, and various kinds of apparatuses using the same.
2. Description of the Related Art
In some of conventional apparatuses for detecting the direction of the line of sight of an eye, first and fourth Purkinje images are utilized, or the positional relationship between light beams reflected by the cornea of the eye, and the pupil of the eye is utilized.
However, in the above-described conventional approach utilizing Purkinje images, since the amount of received light of the fourth image is small, it is difficult to perform detection. In the approach simply utilizing only the relative relationship between light reflected by the cornea of an eye, and the pupil of the eye, detection accuracy is low because the relationship between the images of the cornea and the pupil varies with the individual. Hence, this approach can be used only for monitoring whether or not the direction of the line of sight of an eye is within a certain range.
In conventional perimeters, stimulating light is presented at a particular point near the line of sight of a person to be tested while the line of sight is fixed onto a fixed lamp, and the field of view of the person is measured according to whether or not the stimulating light can be seen. Such a perimeter usually includes a means for monitoring the line of sight of an eye since an error of measurement is produced if the fixed lamp is out of the line of sight of the person. For example, as disclosed in Japanese Patent Publication No. 61-59132 (1986), the direction of the line of sight is measured from the positional relationship between the image of light beams reflected by the cornea of an eye, and the pupil of the eye, and remeasurement is generally performed if the fixed lamp is out of the line of sight.
In the above-described conventional approach, however, since it is very difficult for an eye to be tested to continue to watch the fixed lamp, the line of sight of the eye shifts during measurement, causing an error of measurement of the field of view. Hence, remeasurement is performed if the fixed lamp is out of the line of sight, causing an increase in the time of measurement. As described above, detection accuracy is low using the method of detecting the direction of line of sight from the relationship between the image of light beams reflected by the cornea of an eye, and the image of the pupil of the eye. Hence, this approach can be used only for monitoring whether or not the direction of the line of sight is within a certain range.
In conventional focus apparatuses which can be applied to video cameras, slit lamps, operation microscopes and the like, if a focus sensor is used, the focus sensor is mounted so as to perform a focus operation on a particular position on the picture frame. In another approach, an object is picked up by an image pickup device, and a focus operation is performed using a video signal from the image pickup device.
However, in using a focus sensor aiming at a particular position on the picture surface, if a portion the operator desires to be focused is out of the particular position, this portion is not always focused. In performing a focus operation using a video signal, the desired portion is not always focused since a light portion having a high contrast is focused.